Feel sorry to trouble you, but I'm not fully understand the description

[RainyTunes]

What does the following text mean?
The first can't handle the extra line spacing below last line. The second alone could solve all two problems, with a exception that having a small additional space below last line when last line or the truncated part contains emoji.

看起来您是中国人哈，我再发段中文：
我自己测试的swizzing的解决方案，并没有发现last line下面有extra line spacing，是我理解错了吗？